LibJS: Implement Temporal.ZonedDateTime.prototype.toPlainDate()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/b4ea4e86a74
Pull-request: https://github.com/SerenityOS/serenity/pull/9228
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp

@@ -8,6 +8,7 @@
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Temporal/Calendar.h>
 #include <LibJS/Runtime/Temporal/Instant.h>
+#include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDateTime.h>
 #include <LibJS/Runtime/Temporal/TimeZone.h>
 #include <LibJS/Runtime/Temporal/ZonedDateTime.h>
@@ -60,6 +61,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.valueOf, value_of, 0, attr);
     define_native_function(vm.names.toInstant, to_instant, 0, attr);
+    define_native_function(vm.names.toPlainDate, to_plain_date, 0, attr);
 }
 
 static ZonedDateTime* typed_this(GlobalObject& global_object)
@@ -716,4 +718,31 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_instant)
     return create_temporal_instant(global_object, zoned_date_time->nanoseconds());
 }
 
+// 6.3.47 Temporal.ZonedDateTime.prototype.toPlainDate ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.toplaindate
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_plain_date)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto* zoned_date_time = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let timeZone be zonedDateTime.[[TimeZone]].
+    auto& time_zone = zoned_date_time->time_zone();
+
+    // 4. Let instant be ! CreateTemporalInstant(zonedDateTime.[[Nanoseconds]]).
+    auto* instant = create_temporal_instant(global_object, zoned_date_time->nanoseconds());
+
+    // 5. Let calendar be zonedDateTime.[[Calendar]].
+    auto& calendar = zoned_date_time->calendar();
+
+    // 6. Let temporalDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, calendar).
+    auto* temporal_date_time = builtin_time_zone_get_plain_date_time_for(global_object, &time_zone, *instant, calendar);
+    if (vm.exception())
+        return {};
+
+    // 7. Return ? CreateTemporalDate(temporalDateTime.[[ISOYear]], temporalDateTime.[[ISOMonth]], temporalDateTime.[[ISODay]], calendar).
+    return create_temporal_date(global_object, temporal_date_time->iso_year(), temporal_date_time->iso_month(), temporal_date_time->iso_day(), calendar);
+}
+
 }

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h

@@ -47,6 +47,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(offset_getter);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
     JS_DECLARE_NATIVE_FUNCTION(to_instant);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_date);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.toPlainDate.js

@@ -0,0 +1,23 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.ZonedDateTime.prototype.toPlainDate).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(1625614921000000000n, timeZone);
+        const plainDate = zonedDateTime.toPlainDate();
+        expect(plainDate).toBeInstanceOf(Temporal.PlainDate);
+        expect(plainDate.year).toBe(2021);
+        expect(plainDate.month).toBe(7);
+        expect(plainDate.day).toBe(6);
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Temporal.ZonedDateTime.prototype.toPlainDate.call("foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.ZonedDateTime");
+    });
+});